The present invention relates generally to methods for generating a dynamic pilot symbol structure in spread spectrum communication systems, and in particular to the use of pilot symbols by user equipment in channel estimation. The invention is suitable for use in spread spectrum communication systems using Orthogonal Frequency Division Multiplexing (OFDM) modulation techniques for high speed data communication, such as the proposed long term evolution (LTE) known as super 3G (S3G) system currently being developed by the Third Generation Partnership Project (3GPP) and it will be convenient to describe the invention in relation to that exemplary, but non-limiting, application.
Recent enhancements on packet transmission such as High Speed Downlink Packet Access (HSDPA) and enhanced uplink packet transmission technology such as high speed uplink packet access (HSUPA) have made 3GPP radio-access technology highly competitive. In order to ensure that the competitiveness of this technology continues over a long time frame, a long term evolution (LTE) of 3GPP radio-access technology is being developed. This new technology is known as Super 3G. Important parts of the long term evolution of Super 3G technology includes Radio Access Network (RAN) latency reduction, higher user data rates, improving system capability and coverage, and reducing cost to a network operator. In order to achieve this, an evolution of the radio interface as well as the radio network architecture is being considered. The objective of this evolution is to develop a framework to enable high data rate, low latency and a packet-optimised radio-access technology.
The Super 3G system currently being developed is intended to boost the existing 3G data rate by 10 times, with the target data rate for downlink direction being 100 Mbps and for the uplink direction being 50 Mbps on the 20 MHz transmission bandwidth. The services introduced in Super 3G systems shall be similar to the existing 3G High Speed Downlink Packet Access (HSDPA), Multimedia Broadcast—Multicast Services (MBMS), and High Speed Uplink Packet Access (HSUPA) but with much higher data rate.
In order to achieve such high data rates, a new radio access technology, known as Orthogonal Frequency Division Multiplexing (OFDM) has been introduced together with higher modulation (64-QAM) and coding scheme e.g. turbo or LDPC (low density parity check) coding as well as other features such as Multiple Input Multiple Output (MIMO). The OFDM technology shall provide radio access which allows parallel transmission of data symbols on orthogonal sub-carrier frequencies.
OFDM is a modulation technique that can be used for high speed data communication. OFDM technology for Super 3G is considered to have the following advantages:                high spectral efficiency can be obtained by specific selection of the sub-carrier frequencies by defining the frequency spacing between sub-carriers to be equal to the reciprocal of the OFDM symbol duration.        power efficiency as there no crowding in the signal space        robust to multi-path interference can be obtained by introducing a guard interval between consecutive OFDM symbols in the time domain, and        robust to narrow band interference.        
However, OFDM technology is quite sensitive to impairment such as phase noise, carrier frequency offset, in-phase/quadrature imbalance, phase distortion and linearity issues. These issues always exist in implementation and are computationally complex and expensive to remove. These issues introduce inter-carrier interference, reduce Signal to Interference and Noise Ratio (SINR) and create intermodulation difficulties which contribute to a noise-like cloud surrounding each constellation point. These identified impairments in turn affect the possibility of applying high level modulation schemes and coding schemes, therefore making the target data rate more difficult to achieve.
Accurate channel estimation by user equipment in OFDM technology is also difficult to achieve. Studies have been conducted on appropriate pilot patterns to assist in channel estimation by user equipment, however to date no pilot pattern has been developed which is well suited to the needs of future Super 3G system requirements including wide range of User Equipment (UE) mobility with maximum speed up to 350 km/h.